The present invention relates to a semiconductor device having a semiconductor substrate such as a GaAs substrate and a capacitor formed thereon, a method of fabricating it, and a sputtering apparatus suited to this fabrication method.
Conventional capacitors known in the art include, for example, MIM (Metal-Insulator-Metal) capacitors wherein a dielectric material is sandwiched between two metal electrodes and Schottky capacitors which use Schottky barrier capacitance.
The capacitance C of a MIM capacitor may be expressed in terms of the following equation, where .epsilon..sub.0 denotes a dielectric constant of vacuum, .epsilon..sub.r denotes a dielectric constant of the dielectric material, S denotes a surface area of the capacitor, and d denotes a distance between the electrodes. EQU C=.epsilon..sub.0 .epsilon..sub.r (S/d)
To fabricate a capacitor of high capacitance, a dielectric material of high dielectric constant .epsilon..sub.r may be used, the distance d between the electrodes may be reduced, or the capacitor surface area S may be increased. However, as the use of dielectric materials of high dielectric constant is limited to certain materials, and as there is also a limit to the extent to which the distance d between the electrodes can be reduced, the chosen method is usually to increase the surface area S of the capacitor.
However, attempts to increase the surface area S of the capacitor led to an increase of chip surface area, and this directly results in higher unit costs for chips.